Image pasting, or the creation of a composite image, is usually accomplished by having a system for acquiring individual images that are used to form a combined image with a total field-of-view (FOV) larger than the FOV of the individual images. In most cases, the FOV of the combined image is also larger than the total usable FOV of the x-ray detector used to collect the images. For applications such as full-spine imaging or long-legs imaging, the total coverage of anatomy (e.g., 60–120 cm) exceeds that of most current detectors and film-screen systems.
The process of image pasting may require taking a series of images, one at a time. During this process, a patient is typically asked to stay as still as possible to avoid inconsistencies between subsequent images. This can be uncomfortable for some patients if the process takes an excessive amount of time. Also, an operator imaging a subject may have only a limited amount of time to image the subject, or, alternatively, may have a large number of subjects that the operator must image. A system that could potentially reduce the amount of time that would be needed to image a subject would be preferable.
In image pasting, multiple images are combined to make one continuous image. The ability to accurately join the multiple images often requires that the area of overlap be correctly identified. The higher the resolution of the images, the more crisp the distinctions between structures become, and the easier it is to identify the correct area of overlap. It would be preferable to have a system that could take high quality images.
Further, the ability to identify the correct area of overlap can often be increased when the areas to be overlapped are substantially the same. This is not always possible, since some objects (such as a patient's diaphragm) may tend to move between images. If one of these objects is in the region of overlap then a pasted image would not appear continuous because the moving object could potentially be captured in two different positions. Also, combining the images could be made more difficult because there would be no uniform region of overlap. An image pasting system that could avoid placing these objects in the region of overlap would be preferable.
Additionally, an image pasting algorithm can be used to automate the joining of images. Since images may overlap in a variety of areas, an algorithm could potentially have to search large portions of an image looking for an appropriate area of overlap. Such a system would likely not work as efficiently as possible. A system that can provide a starting point for an image pasting algorithm to locate the region of overlap is desirable.
Also, some parts of a subject may be more sensitive to x-rays than other parts of the subject. For instance, a patient's heart or gonads may be more sensitive to x-ray radiation than other parts of a patient. This may be even more true when the patient is a developing child. In a baggage/package handling context, camera film in a person's travel bag or package may be more sensitive to x-ray radiation than other contents of the bag/package. While these objects can handle x-ray radiation, it is often better to reduce the amount of radiation to which these areas are exposed. In an image pasting application, it would be preferable to exclude these dose-sensitive areas from the region of overlap (i.e. those areas in a region to be imaged that cover avoidable structures that are more sensitive to X-ray radiation than the other potentially avoidable structures in the region to be imaged).
Even more, when detectors with circular input regions are used, the length of overlap necessary to obtain a sufficient total area of overlap to allow accurate joining is greatly increased as compared to the length required for detectors with substantially rectangular input areas. This extra required length can make it significantly more difficult to avoid placing a structure (such as a dose sensitive-structure) in the area of overlap. Thus, it would be preferable for the x-ray detector to have a substantially rectangular area of overlap.
Also, certain medical uses of x-ray detectors take images that start and/or stop just shy of areas that should not be exposed to x-rays if that area is not to be imaged. For instance, one procedure is aimed at obtaining an image of an area starting just below a patient's head and ending just above the patient's waist, thus, the area to be imaged is bracketed by dose-sensitive organs (the organs of the head, and the gonads). In this case, it would be undesirable to allow x-rays to extend above or below the area to be imaged. Thus, it would be preferable to have an x-ray system that can control an x-ray source such that the x-rays do not extend past the area to be imaged.
The teachings herein below extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the above-mentioned needs.